Gradient valence-distributed vanadium oxygen hydrate hybrid induces high performance aqueous zinc-ion batteries

Abstract

Gradient valence-distributed vanadium oxygen hydrate hybrid (G-VOH) nanowires are designed by one-step hydrothermal synthesis for aqueous zinc-ion batteries. It is mainly constructed by superficial NH₄⁺-intercalated VOH ((NH₄)₂V₁₀O₂₅·8H₂O, named as NVOH) and inner deeper vanadium reduction VOH (V₃O₇·H₂O, named as VOH). In the unique nanostructure, both NVOH and VOH are active matrices involved in the Zn²⁺ electrochemical reaction. Moreover, the outer NVOH functions as a Zn²⁺ transport framework to provide fast Zn²⁺ transport capability for the inner VOH. Additionally, the gradient vanadium valence distribution in hybrids enhances the vanadium multi-valence redox kinetics, resulting in significant improvement for the Zn²⁺ storage capacity. Meanwhile, NVOH also functions as a framework support to suppress the inner VOH crystal structure conversion during the charge/discharge process, facilitating its electrochemical stability. Thus, the G-VOH nanowires obtain a high specific capacity of 434 mA h g⁻¹ at 0.1 A g⁻¹, as well as long cycling stability with 86% capacity retention at 2 A g⁻¹ after 1500 cycles. Moreover, the assembled quasi-solid-state G-VOH||Zn batteries achieve a superior specific capacity of 241 mA h g⁻¹ at 1 A g⁻¹ with a capacity retention of 74% after 500 cycles. The strategy of the preparation of gradient valence-distributed vanadium oxygen hydrate provides a new idea for the development of cathode materials for aqueous zinc-ion batteries.